The present invention relates to a method and apparatus for recording information in an information recording medium by radiation of an energy beam, or more in particular to an information recording method very effective for a phase change optical disk and an information recording apparatus using such an information recording method.
A conventional method of recording and erasing information in a rewritable record film is disclosed, for example, in JP-A-62-175948 (laid open Aug. 1, 1987), which uses a magneto-optical disk of an exchange couple double-layered film as a record film. Another conventional method for recording and erasing information in a rewritable record film is disclosed in JP-A-62-259229 (laid open Nov. 11, 1987), which uses a record film for a phase change optical disk capable of high-speed erasure by crystallization within substantially the same time as the laser radiation time for recording. In these cases, the power of an energy beam is alternated between at least two levels both higher than the read level, i.e. between at least a high power level and an intermediate power level. This method has the advantage that what is called “overwrite” is possible with new information recorded while at the same time erasing the existing one. Also, as disclosed in JP-A-62-259229 described above and JP-A-3-185629 (laid open Aug. 13, 1991), a record mark can be prevented from assuming a shade such that the rear portion of the record mark is wider than the front portion thereof by changing the energy beam between three levels including a high power level, an intermediate level and a power level lower than the intermediate level.
Research is under way for increasing the density of a rewritable digital video disk (DVD-RAM) using a phase change record film. In an optical disk device for performing the mark edge recording in a phase change record film such as the DVD-RAM, substantially the same temperature and substantially the same cooling rate are required for recording at every part of the outer edge where the record film is melted for forming a record mark or a mark portion in order to prevent a mark shape distortion and residue. The various record waveforms thus far known, however, fail to meet these conditions sufficiently and the feasible recording density is limited. Especially with the DVD-RAM having a recording capacity of 4.7 GB or more, the distance between centers of laser beams radiated onto a recording medium to form adjacent two mark portions thereon is small as compared with the diameter of the laser beam spot, with the result that light is considerably overloaded in distribution. It is necessary to prevent a record mark distortion caused by this phenomenon. In the case where the space portion between mark portions is short, the record mark edge position of a reproduced signal waveform shifts due to the fact that such mark portions cannot be resolved by the beam spot. This inconvenience is also required to be prevented.
With the increase in digital signal processing rate in recent years, demand has been rising for an increased recording and reproduction rate of an information recording apparatus. In order to meet this demand, a higher relative speed between an energy beam and an information recording medium has become crucial. Therefore, an information recording method is required which is capable of performing a stable recording operation even in the case where the relative speed between an energy beam and an information recording medium is high.